1. Field of the Invention
The present invention relates to a magnetic encoder for detecting a magnetic flux, which is generated by a scale coil and cyclic changes in a measuring direction, by using a detection coil which relatively moves in the measuring direction with respect to the scale coil, and for calculating an amount of relative displacement according to increase and decrease in the detected amount of magnetic flux.
2. Description of the Related Art
An encoder for detecting an amount of relative displacement between two objects by utilizing a periodical change of a predetermined physical quantity has been known. That is, first, a cyclic change in a movement direction of the predetermined physical quantity is formed by using a scale fixed to one of the objects, which relatively move with each other. This cyclic change is detected by using a sensor fixed to the other object. Then, the number of cyclic intervals is counted to thereby calculate the amount of relative displacement between two objects.
Although the encoder can detect the amount of relative displacement between two objects, the encoder cannot detect directly the relative positions thereof. That is, this encoder can detect only relative positions thereof to be defined as amounts of displacement thereof from a reference position. Meanwhile, there has been known an absolute encoder provided with a plurality of scales respectively having different cyclic intervals and enabled to detect an absolute position of two objects within a cyclic interval, which is a least common multiple of the different cyclic intervals.
A related art magnetic encoder that is adapted to function as an absolute encoder, employs a configuration in which a plurality of first scale coils 14xe2x80x2 arranged at predetermined cyclic intervals and a plurality of second scale coils 16xe2x80x2 arranged at other cyclic intervals which are different from those of the first scale coils 14xe2x80x2 are connected in a one-to-one relation by using connecting wires 18xe2x80x2,as shown in FIG. 7. The first scale coils 14xe2x80x2 form a sequence of magnetic fluxes at first cyclic intervals in response to signals received by the second scale coils 16xe2x80x2. Conversely, the second scale coils 16xe2x80x2 form a sequence of magnetic fluxes at second cyclic intervals in response to signals received by the first scale coils 14xe2x80x2. Thus, electric current flows through each of the connecting wires 18xe2x80x2 provided between the first scale coils 14xe2x80x2 and the second scale coils 16xe2x80x2.
In the related art magnetic encoder having a scale of a configuration in which the first scale coils 14xe2x80x2 and the second scale coils 16xe2x80x2 arranged at different cyclic intervals are connected by using connecting wires 18xe2x80x2, electric currents flowing through two conductors, which constitute each of the connecting wires 18xe2x80x2, in opposite directions and weaken each other. Thus, the signal levels of the detected signals are degraded. Meanwhile, the first scale coils 14xe2x80x2 and the second scale coils 16xe2x80x2 are arranged at different cyclic intervals. Therefore, for example, as shown in FIG. 7, when each of the connecting wires 18xe2x80x2 connects between a center of a side of each first scale coil 14xe2x80x2 and a center of a side of a corresponding one of the second scale coils 16xe2x80x2, the side of the first scale coil 14xe2x80x2 and the side of the second scale coil 16xe2x80x2 being opposite to each other, the length of the connecting wires varies with the position on the scale. In the case that the length of the connecting wires varies therewith, the degree of degradation in the signal level of the detected signal also varies therewith. Thus, the relative art magnetic encoder has a problem in that the signal level of the received signal changes with the position of the detection coil on the scale.
The invention is accomplished to solve the aforementioned problem. Accordingly, an object of the invention is to provide a magnetic encoder enabled to reduce change in the signal level of a received signal, which depends upon the position of a detection coil on a scale.
To solve the foregoing object, according to the invention, there is provided a magnetic encoder adapted so that a plurality of connecting wires, which connect a plurality of first scale coils arranged in the measuring direction at first cyclic intervals and a plurality of second scale coils arranged in the measuring direction at second cyclic intervals, which are other than integral multiples of the first cyclic interval have a nearly equal length. Thus the signal level of the reduced signal is uniformed among the connecting wires. Consequently, change in the signal level, which depends on the position of the detection coil on the scale, can be reduced.
Further, preferably, a direction, in which the connecting wires extend, is nearly perpendicular to the measuring direction. Thus, the length of the wires can be decreased. Consequently, the reduction in the signal level can be decreased.
Moreover, preferably, the cyclic intervals, at which the connecting wires are arranged in the measuring direction, are set to be constant. Thus, the finding of the influence of the magnetic flux caused by the connecting wires can be facilitated.